Supply of energy resources across the globe is becoming scarce. Various alternative energy sources have been explored, including solar, wind, tidal, and geothermal. Because all of these alternative sources may be unpredictable, various systems have been implemented to accurately and consistently estimate and model the energy output and characteristics of these sources.
Geothermal energy is thermal energy generated and stored in the Earth. From hot springs or other thermal vents, geothermal energy can be extracted and converted into electrical energy. For geothermal, the measurement of void fraction from each geothermal well/vent/spring enables the operators of geothermal wells to calculate the total enthalpy of the two-phase fluids produced from the well, and hence, estimate the energy output. Void fraction or porosity is a measure of the void (i.e., “empty”) spaces in a material, and a fraction of the volume of voids over the total volume. For example, the void fraction can be expressed as between 0 and 1 or as a percentage between 0 and 100%. A pump can extract both steam and water (e.g., brine) out of a geothermal vent, creating a gas-liquid two-phase flow. The void fraction can be defined as the fraction of the flow channel volume that is occupied by the gas phase (e.g., steam) or, alternatively, as the fraction of the cross-sectional area of the channel that is occupied by the gas phase.
Conventional techniques of measuring void fraction mostly involve taking the geothermal system out of commission temporarily. For example, a conventional method involves redirecting the output flow from a geothermal well into a separator/silencer assembly to measure the ratio of steam flow and water flow. For another example, the output flow may be redirected into a pressure-controlled pipe to estimate the void fraction. These techniques are disruptive to the energy production cycle of a geothermal power plant.
Recent developments led to a technique of measuring the void fraction via precise metered injection of liquid and vapor phase tracers into the two-phase production pipeline and sampling each phase downstream of the injection point. While this technique does not disrupt the production pipeline, this technique does require additional lab work and does not provide instantaneous feedback of the geothermal well's performance.